Rations are nutritional supplements designed to nourish the body in place of normal food. They are often used in combat situations and other emergencies, but their taste often leaves much to be desired.
Carmen Davila a colonist on Melona IV, saved a ration of dried chicken curry for a very special occasion. (TNG: "Silicon Avatar")
In the United Federation of Planets, the rations used are called emergency rations, although many nicknames exist for them. Although use of these rations are considered by many Starfleet officers to be a necessary evil, Julian Bashir developed a candy bar with superior nutritional value. (DS9: "The Siege") Starfleet rations were specifically, "concentrated vitamin enriched nutritional supplements." (VOY: "Innocence")
During the USS Voyager's time in the Delta Quadrant, Captain Janeway and her crew were forced to invent a system of replicator rationing in order to save energy and supplies. (VOY: "Meld")